Patent Literature 1 contains disclosure with regard to detection of leakage of hydrogen when a fuel cell system stops generation of power. Patent Literature 2 contains disclosure with regard to detection of leakage of hydrogen when a system is in a dormant state. Patent Literature 3 contains disclosure with regard to a system for detecting an abnormality such as leakage of hydrogen. According to the art disclosed in Patent Literatures 1 to 3, a device for detecting leakage of hydrogen demands that its power supply is always turned on.